Along with the recent reduction in size and thickness of portable wireless terminals, some techniques using a case made of metal to ensure the rigidity of the terminals have been published.
Furthermore, along with the recent reduction in size and thickness of portable wireless terminals, the wireless functions mounted in the portable wireless terminals have been increased in number and increasingly sophisticated. This results in the necessity to mount a plurality of antennas in a small and thin metal case, while the distance between each antenna and the metal is extremely shortened due to limitations in mounting space of the antennas. Generally, if a metal is disposed near an antenna, the antenna characteristics are significantly degraded, which causes a problem that the antenna fails to function as a wireless terminal.
To solve such a problem, a technique is disclosed in which an elongated notch (slot) is formed in a metal case and the slot is allowed to operate as an antenna, as a technique for allowing an antenna to operate even when the antenna is disposed near a metal. A slot antenna typically has narrow-band characteristics. Accordingly, a technique for achieving a wide band by generating multiple resonances using a plurality of slots is well known.
Patent Literature 1 discloses an antenna apparatus having a plurality of slots formed therein to achieve multi-resonance characteristics. The antenna disclosed in Patent Literature 1 is composed of a notch antenna having a notch formed in a range from a substrate to an edge, and a parasitic notch antenna which is slightly shorter than the notch antenna and has a notch formed in parallel with the notch antenna.
In Patent Literature 2, two conductor plates are provided to face each other, and the conductor plates are connected together on one side thereof via another conductor plate. One of the two conductor plates has a gap portion (slit) with an open end formed at a side opposite to the side connected to another conductor plate. Capacitors C1 and C2 are disposed at locations sandwiching the gap portion, and are connected between the two conductor plates. The antenna disclosed in Patent Literature 2 achieves two resonances in regions on both sides of the gap portion of the conductor plate having the gap portion, and adjusts the resonances using the capacitors C1 and C2.